(1) Field of the Invention
This invention relates to a light-sensitive composition useful for a presensitized plate from which a planographic printing plate is to be prepared, and particularly to a novel photopolymerizable composition which is wholly or almost wholly insusceptible to oxygen-induced inhibition of polymerization when a printing plate is prepared from a presensitised plate comprising the composition.
(2) Description of the Prior Art
There have been made many attempts to use photopolymerizable compositions as an image forming layer suitable for a presensitized plate. For instance, there have been known various compositions such as a basic composition comprising an organic solvent-soluble polymer, an ethylenically unsaturated addition polymerizable compound and a photopolymerization initiator as described in U.S. Pat. No. 3,458,311, a composition comprising an organic solvent-soluble polymer to which an unsaturated double bond is introduced to thereby have its hardening property improved as described in U.S. Pat. No. 3,796,578, a composition comprising a novel photopolymerization initiator as described in U.S. Pat. Nos. 3,549,367 and 3,751,259 and British Patent 1,388,492, etc. Some of these have been put into practice but it has been impossible, from the practical point of view, to use any of these compositions as a light-sensitive layer of a presensitized plate unless an oxygen barrier comprising a water-soluble resin is provided on the surface of the light-sensitive layer because the polymerization thereof is remarkably inhibited by oxygen during image-wise exposure. Attempts have been made to reduce the polymerization inhibition by oxygen by adding a negative working diazo resin to the photopolymerizable compositions, as described in Japanese Patent Applications (OPI) 206825/1984, 53836/1984, 178449/1984 and 196230/1982 (The term "OPI" as used herein refers to a "published unexamined Japanese Patent Application".) and U.S. Pat. No. 4,316,949. However, all of these attempts give only insufficient results.